[Spaceships] Homebrew: Alternate Spin Tethers

[DaltonS]

Another way to look at spin tethers (GURPS Spaceships 7 p.22) involves its tensile strength and two ships of (possibly) unequal masses. Given that Mn and Gn are the respective mass (in tons) and gravities of ship "n" and T is the tensile strength of the tether in tons load:

T/2 = G1*M1 = G2*M2

The mass of the tether would be T/20,000 tons (possibly adjusted by TL to reflect changes in materials), the cost $10*T and the minimum length would be (G1+G2)*50 yards†. It may be longer and thinner and spin more slowly as long as the stress didn't exceed its tensile strength. Please note that

1. mass and cost of this design feature only requires knowing the data for one ship,
2. the external cradle should be installed on the larger ship,
3. the center of spin would be Gn/(G1+G2) times the tether's total length from ship "n", and
4. since it is carried as cargo in a hold or hangar bay, its mass can be ignored.

† GURPS Vehicles Expansion 1 from 3E recommends a minimum 100 yard/G spin radius (twice the 4E value) with three times that considered nominal. Also, the cost there was $10 per pound of total loaded mass, or $20K/ton.

Example: A 0.4 G spin tether for an SM+6 ship heading to Mars (local gravity .38 G) would have a tensile strength of 80 tons, cost $800 and mass 8 lbs. If attached to another SM+6 ship, its minimum length would be 40 yards (80 yards by 3E rules). If an SM+5 ship was attached, the g-force in the second ship would be 0.4*100/30=4/3 Gs and the minimum tether length would be 173 1/3 yards or 520 feet.

Dalton “who loves putting a new spin on things” Spence